There is known a vehicle power source system which includes a high-voltage battery and high-voltage system equipment and in which the high-voltage battery and the high-voltage system equipment are cooled by a single cooling circuit (for example, refer to Patent Literature 1). Additionally, there is also known a cooling circuit which includes two high-voltage system equipment cooling units which are disposed in series and in which two pieces of high-voltage system equipment (a DC-DC converter and an inverter) are cooled at the same time by those high-voltage system equipment cooling units (for example, refer to Patent Literature 2). Further, there is known a cooling circuit in which in cooling a plurality of high-voltage battery modules by a single cooling system, the high-voltage battery modules can be cooled selectively through a flow path switching control (for example, refer to Patent Literature 3).